Recent years, three new major techniques for rare earth sintered magnet (comprising R2Fe14B-type main phase) have been rapidly applied to the technical processes of mass production, the details are as follows:
1. Magnet manufacturing process with low oxygen content: reducing the oxygen content of the magnet that deteriorates the sintering property and coercivity as much as possible;
2. Raw material manufacturing process: the raw material alloy is manufactured by strip casting method as represented, wherein at least one part of the alloy is manufactured by quenching method;
3. By adding a minor amount of Cu, it is capable of obtaining a higher value of coercivity within a wider temperature range, and mitigating the dependency of coercivity and quenching speed (from public report JP2720040 etc.).
It is easily capable of acquiring an extremely high property by the additive action of increasing the amount of Nd-rich phase in the crystal grain boundary and the dispersibility after combining the three new techniques for mass production.
However, the number of low melting liquid phase is increased during the sintering process as Cu is added into the low-oxygen magnet; and the shortages of easy occurrence of abnormal grain growth and the significant decreasing of the squareness (SQ) arise while the sintering property is significantly improved at the same time.